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I am using Qt4 to build an application and for some reason I want to keep it proprietary. Qt4 is released under LGPL, does that force me to release the code to my application. I ask this question because I am finding it difficult to understand the LGPL license.

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    As far as I know, Qt relatively recently underwent licensing changes that allowed you to use it in close source commercial products. It didn't used to be okay, which is why a great many folks used to prefer GTK
    – RobotHumans
    Sep 28, 2012 at 2:46
  • @aking1012: Not that recent. Mathematica has been using Qt for a few years at least.
    – Mechanical snail
    Sep 28, 2012 at 4:45
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    @Mechanicalsnail IIRC it had to do with cost of licensing previously. January 2009 or so is when it went LGPL according to this blog post: successfulsoftware.net/2009/01/14/… for the decade previous it was pay to be used commercially.
    – RobotHumans
    Sep 28, 2012 at 4:54
  • So you all are saying I can use it to make my own commercial product but the catch is I need to have the LGPL Licence with my binary?
    – Alwin Doss
    Oct 1, 2012 at 2:31
  • Indeed. Note also that the binary can not have Qt statically linked, as that would mean it is considered a derivative work instead of something using it - which would mean that you would have to either open-source your app, or pay for the proprietary-licensed Qt version. Dynamic linking and including the LGPL is all you need to do.
    – user64152
    Oct 4, 2012 at 6:50

2 Answers 2

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Yes.

"The main difference between the GPL and the LGPL is that the latter allows the work to be linked with (in the case of a library, 'used by') a non-(L)GPLed program, regardless of whether it is free software or proprietary software.

Source:Wikipedia

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    This is a great answer. To make it even better, you can try to expand with more examples.
    – nanofarad
    Nov 23, 2012 at 13:46
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In addition to @user64152's answer I have to add one more thing. If along with proprietary you also intend to make a commercial product and modify the Qt libraries, you have to buy the Qt Commercial License in order to be able to sell your product.

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  • This is not true. LGPL (which Qt is released) Allows commercial/closed source applications as long as you do not modify the qt libraries or if you do making them available to the public. But just the LGPL'd libraries.
    – Vassilis
    Feb 9, 2015 at 10:40
  • Yes, I didn't express myself clear enough. Will add this to my answert. Thanks!
    – rbaleksandar
    Feb 9, 2015 at 13:28

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